Post-translational modifications of Hsp90 that impact drug efficacy

热休克蛋白90（Heat shock protein 90，Hsp 90）是一种分子伴侣，它是许多信号蛋白稳定和功能所必需的，这些信号蛋白通常在癌细胞中被激活、突变或过表达，并且是癌细胞增殖和存活的基础。热休克蛋白90是一种构象灵活的蛋白质，它与一组不同的辅分子伴侣相关联，这取决于氨基末端结合口袋的ATP或ADP占用率。Hsp 90自身的核苷酸交换和ATP水解，在辅分子伴侣的协助下，驱动Hsp 90分子伴侣机器结合、分子伴侣和释放客户蛋白。Hsp 90分子伴侣机器的循环对其功能至关重要。虽然ATP结合和水解已经令人信服地参与调节Hsp 90循环，越来越多的证据表明，Hsp 90的各种翻译后修饰，包括磷酸化，乙酰化和其他修饰，提供了额外的重叠或平行水平的调节。更全面地了解这些不同的蛋白质修饰是如何在细胞水平上调节和相互作用以调节Hsp 90分子伴侣活性的，这对于设计抑制这种医学上重要的分子靶点的新方法至关重要。调节Hsp 90的不同翻译后修饰的信号通路的协调是非常可能的。理解各种修饰之间的相互作用无疑是一项艰巨的任务，但这些知识将大大增加我们对Hsp 90功能在细胞复杂环境中如何调节的理解。这些信息可能提供一种独特的方法，在癌细胞中特异性阻断Hsp 90的功能，因此将是一个重要的考虑因素，在设计Hsp 90抑制剂与其他分子靶向药物的临床试验。对翻译后修饰在调节Hsp 90功能中所起作用的更透彻理解肯定会提高此类联合治疗的有效性。 热休克蛋白90受到一系列的翻译后修饰，影响其功能，包括乙酰化。组蛋白去乙酰化酶（HDAC）抑制剂和HDAC 6的敲低诱导Hsp 90乙酰化并抑制其活性。然而，直接确定热休克蛋白90乙酰化的功能后果一直等待映射的具体网站。我们已经证明Hsp 90 K294是乙酰化的。K294的突变分析表明，其乙酰化状态是客户蛋白和辅伴侣结合的强决定因素。在酵母中，与WT或模拟组成型乙酰化的突变体相比，不能在K294处乙酰化的Hsp 90突变体具有降低的活力和伴侣功能。这些数据表明，K294的乙酰化/去乙酰化在调节Hsp 90分子伴侣循环中起着重要作用。进一步的研究集中在Hsp 90中特定氨基酸的磷酸化以及这些翻译后变化对Hsp 90对抑制性药物亲和力的影响。

Heat shock protein 90 (Hsp90) is a molecular chaperone required for the stability and function of many signaling proteins that are often activated, mutated or over-expressed in cancer cells and that underly cancer cell proliferation and survival. Hsp90 is a conformationally flexible protein that associates with a distinct set of co-chaperones depending on ATP or ADP occupancy of an amino-terminal binding pocket. Nucleotide exchange and ATP hydrolysis by Hsp90 itself, with the assistance of co-chaperones, drive the Hsp90 chaperone machine to bind, chaperone, and release client proteins. Cycling of the Hsp90 chaperone machine is critical to its function. Although ATP binding and hydrolysis have been convincingly implicated in regulating the Hsp90 cycle, growing evidence suggests that various post-translational modifications of Hsp90, including phosphorylation, acetylation, and other modifications, provide an additional overlapping or parallel level of regulation. A more complete understanding of how these various protein modifications are regulated and interact with each other at the cellular level to modulate Hsp90 chaperone activity is critical to the design of novel approaches to inhibit this medically important molecular target. Coordination of signaling pathways that mediate distinct post-translational modifications of Hsp90 is highly likely. Understanding the cross-talk between various modifications will no doubt be a difficult undertaking, but such knowledge will add greatly to our appreciation of how Hsp90 function is regulated in the complex milieu of the cell. Such information may provide a unique approach to specific interdiction of Hsp90 function in cancer cells and will thus be an important consideration in designing clinical trials of Hsp90 inhibitors in combination with other molecularly targeted drugs. A more thorough understanding of the role that post-translational modifications play in modulating Hsp90 function will certainly improve the effectiveness of such combination therapies. Hsp90 is subject to an array of posttranslational modifications that affect its function, including acetylation. Histone deacetylase (HDAC) inhibitors and knockdown of HDAC6 induce Hsp90 acetylation and inhibit its activity. However, direct determination of the functional consequences of Hsp90 acetylation has awaited mapping of specific sites. We have demonstrated that Hsp90 K294 is acetylated. Mutational analysis of K294 shows that its acetylation status is a strong determinant of client protein and cochaperone binding. In yeast, Hsp90 mutants that cannot be acetylated at K294 have reduced viability and chaperone function compared to WT or to mutants that mimic constitutive acetylation. These data suggest that acetylation/deacetylation of K294 plays an important role in regulating the Hsp90 chaperone cycle. Further studies are focusing on phosphorylation of specific amino acids in Hsp90 and of the affect of these post-translational changes on Hsp90 affinity for inhibitory drugs.